varying water temperature and thermo fan

Started by DJH, October 29, 2022, 04:09:30 PM

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Hi all

A slightly strange issue seems to have come up with my twin spark the last couple of months.  It used to sit pretty steady at an indicated 80 for the water temperature with the thermo fan keeping it somewhere between about 83 and 78.  Now it will stay around 80 for about 20 minutes of driving and then if Im in traffic it will go just above 90 before the thermo fan kicks in - brings it back to around 83 eventually (a bit disconcerting and especially with warmer weather around the corner).  It doesnt always do this though - every now and again it goes back to its usual self.

The water pump is new (as the engine was reconditioned).  The belts all seem good.  Its got a new radiator, expansion tank is fine, new cap for the expansion tank, new thermostat and I also put in a new switch into the radiator for the thermo fan.

Anyone seen something like this before and have any tips?  I think Im down probably to the relay switch but Im not sure if they behave with such variation (and of course they are of a type that dont seem to be made anymore).



You will find all the answers you need and the degrees of how far you want to go right here.

Bear in mind that the temperatures you are experiencing are not extreme. You could use an independent thermometer to check the calibration of your instruments to provide some assurance of the facts as well.
Transaxle Alfas Haul More Arse.


Thanks MD

Its really the variability and intermittent nature of it that has me stumped.  I agree that the temp gauge probably isnt to be entirely trusted, but it does hold a pretty steady high 70's when the thermostat is doing its thing.



If you read the linked post, you should have realised that there is a design issue with the radiator itself. You are not likely to change the status quo unless you install a radiator for local conditions. Not everybody's cup of tea.

Having said that, it is a beautifully engineered radiator using all the latest internal spirals to scrub as much heat out of the coolant as possible. Regrettably the fins are too dense for sufficient airflow in stop start traffic and cannot dump the heat out fast enough. That is why you are getting a higher temp and the thermo switch is kicking in.

Remember for efficient combustion higher temps are more effective provided the system doesn't boil. Running your engine at 80* is a little cold and less would cause inefficiency and unnecessary wear. Running between 85-90 should be fine.

If your engine consistently runs over 100*C, Check timing, Check fuel mixture for lean running.Check thermo fan is getting a good power supply. Probably drawing in excess of 18amps. The relay is unlikely a cause as it is generally either working or not.

Using glycol in the coolant raises the boiling point and if your radiator cap is holding pressure, you really don't have a major problem. Fan cycling is perfectly normal.
Transaxle Alfas Haul More Arse.